Coordination circuit



Nov. 29, 1955 J. MILLMAN 2,725,553

COORDINATION CIRCUIT Original Filed Jan. 15, 1946 2 Sheets-Sheet l |o soI RADAR RECOGNITION I SYSTEM SYSTEM I I6 76 MULTI- II I Q J U i 65V|9RATR RECEIVER I 'MULTIVIBRATOR 29 GATE 1m I We 7I\ 1 MULTIVIBRATORSELECTOR I I II 30 I I II as Ll'U'qo 3| L I I INVERTER a OATHODEMULTIVIBRATOR RECTIFIER FOLLOWER 1 I I I II I 32 I M. I I

I I 3| I I I l I I i I 38 I I J U a? I I I MULTI- I I 23 I 95 93 92 1 II I 94 r I I I I lNl/ENTOR JAcos MILLMAN 477' RNEYS J. MILLMANCOORDINATION CIRCUIT Nov. 29, 1955 2 Sheets-Sheet 2 Original Filed Jan.15, 1946 A77 IVEYS N MA m ML W M B I lo 0 A J 2 79 3 9 .6. m m m m n m MH w 4 4 4 5 6 Unite States Patent 2,725,553 Patented Nov. 29, 1955 diceCOORDINATION CIRCUIT Jacob Millman, Flushing, N. Y., assignor, =by mesneassignments, to the United States of America :as :represented by theSecretary of the Navy 7 Claims. ((31. 343-65 This invention relates toelectric synchronizers and more particularly to a circuit for derivingan electric pulse of a relatively low repetition rate from a highperiodicity recurrent-pulse signal and for timing each low repetitionrate pulse to coincide with a pulse of the higher repetition rate.

This vapplication is a division of copending application, Serial No.641,335, filedJanuary .15., 1946, now U. 5. Patent No. 2,605,408, issuedJuly 29, 1952, entitled Coordination Circuit.

The multivibrator is commonly employed as .a timing device wherein thesignal output of the multivibrator is of a repetition rate which is asubmultiple of .the repetition rate of an input synchronizing 'or timingsignal. Inherently, therefore, the multivibrator .is limited in itsfunction as a timer or frequency divider to applications involvingintegral repetition rates.

The present invention overcomes this limitation and provides a circuitfor generating .an electric pulse signal of a relatively low repetitionrate Ithat is nonintegral with .a pulse of higher repetition rate fromwhich it is derived.

An object of this invention is to provide-a circuit which :acts as afrequency divider and derives an electric pulse .ofa nonintegral andrelatively low repetition rate from a pulse of a higher repetition rate.

vAnother-object is to provide acircuit for synchronizing each pulse of asignal of a relatively low average repeti tion rate to a pulse of asignal of a relatively high and nonintegral repetition rate.

A further object is to provide a synchronizer in which a control signalof relatively low frequency is combined with a pulse signal of a highand nonintegral repetition rate so that there is a resultant outputpulse signal having an average repetition rate equal to the controlfrequency and each pulse of which is synchronous with a pulse of thehigher repetition rate signal.

These and other objects and features of this invention will becomeapparent upon a consideration of the following detailed description whentaken together with the accompanying drawings, the figures of whichillustrate a typical embodiment of this invention.

Fig. 1 is a block diagram of a radar system and a cooperatingrecognition system together with a system for coordinating theiroperation, including a syndhron'izer or frequency divider according tothis invention; and

Fig. 2 illustrates the wave forms at various points of the circuit ofFig. 1 as a functionof time.

The illustrative use of this invention as "shown in Figs. 1 and 2relates to a radar system having an A-scope" indicator type ofpresentation on which the radar output gives a positive deflection, theposition of the deflection along the base line being proportional torange. Recognition signals are also displayed on the A-scope with anegative deflection on a horizontal sweep which is vertically displacedfrom the radar sweep so that confusion is avoided. The recognitionsystem includes an interrogating transmitter and a receiver forreception of recognal .12, the modulator of radar nition signals fromfriendly targets having equipment responding to the interrogatingsignals. The antenna beam of the recognition system is broader than thatof the radar system. To provide the necessary directivity for therecognition antenna and unmistakable association of radar target andrecognition signals, the recognition antenna beam is lobe switched, theechoes returned for each of two lobes being horizontally displaced onthe A-scope and their amplitudes matched as an index of the centering ofthe beam on the target under which the first recognition echo appears.

in this illustrative embodiment of the invention, the horizontal sweepsfor the A-scope are generated by the radar system, operating at arepetition frequency of 806 pulses per second. The recognitionsystem-operates from a source of 6G cycle current, has a lobe switchingfrequency of 60 cycles and interrogates, therefore, at a rate of pulsesper second. The synchronizer of this invention is the heart of thecoordination system and utilizes a full-wave rectified 6O cycle wave ora 120 cyclecontrol frequency, during each cycle of which one trigger outof the series of radar modulator pulses is selected to trigger theinterrogator. Simultaneously, the other units, of the coordinatingsystem provide blanking for the radar receiver, unblanking of therecognition receiver, and vertical displacement of the horizontal sweepon the A-scope flIl order to set apart the recognitiomdisplay trace fromthat of the radar system. Also, on alternate interrogator pulses, theA-scope sweep is displaced horizontally .so that the signal return fromeach lobe of the recognition system antennabeam may be seenseparatelyrfor matching of amplitudes.

Referring to Figs. 1 and 2, radarisystem ll) includes the conventionalunits, a transmitter with pulse modulator, receiver, antenna, horizontalsweep generator, and the -scope type cathode ray tube indicator 11. Fromtermisystem ii) supplies a series of negative triggers 16 to unit 17,comprising inverter'and cathode follower stages. Positive triggers 18are produced at the output of unit 17 and supplied -to synchronizer unit19. Synchronizer d9 receives triggers 18 which are the high-periodicityrecurrent pulse signal input derived from radar system ll), at a firstinput circuit connected to terminal 14. The signal at terminal 14 Willbe referred to hereafter as the input signal. The multivibrator of unit20 is a conventional 'two-toone divider completing one cycle andstarting another of square wave 21 when triggered by every other pulseof output 18. Square wave 21 is difierentiated -by capacitor 22 andresistor 23 in series to ground and the resultant output 26, withalternate positive and :negative triggers, appears at terminal 27. Fromterminal 27, triggers 26 are supplied to selector Z5 and also to unit'28 which will be described later.

'Synchronizer 19 has a second input circuit connected to terminal 36 towhich is supplied a periodic control signal hereafter referred to as thecontrol signal, having a periodicity substantially lower than the inputsignal applied to terminal 14. lower source 29 supplies 60 cycle A. C.current shown in wave 30 which is full-wave rectified by rectifier 31.The output 'of rectifier 31 is the 120 cycle wave 32 which is applied toterminal 36 and coupled through capacitor 33, where it loses its D. C.component as shown in wave 34, thereafter being supplied to selector 25.

Selector 25 comprises vacuum tube repeater meanscontrol grid. The outputis taken from the cathode circuit and reproduces only those few positivetriggers of wave 26 which occur during each cycle of wave 34 when thescreen grid of the tube of selector 25 is also positive. The output ofselector 25 is wave 37, whose first trigger during each cycle of wave 34is selected to trigger a pulse-responsive means comprising multivibrator38. The square wave output 39 of multivibrator 38 is a recurrent-pulsesignal which is differentiated by capacitor 40 and resistor 41 connectedin series to ground, wave 42 appearing at their junction withalternately positive and negative triggers. Multivibrator 46 istriggered by the positive triggers only of wave 42 and generates squarewave 47. Square wave 47 is applied to the control grid of the pentode ofselector 48 and positive triggers 18 are applied to the screen grid ofthe pentode of selector 48 through coupling condenser 104. The resultantoutput negative triggers 49 are applied to unit 50, comprising inverterand cathode follower stages, whose output is wave 51. Each pulse of wave51 triggers multivibrator 52, generating square wave 53.

Square wave 47, trigger wave 51, and square wave 53 also constituteblanking and unblanking gates and triggers for coordinating theoperation of recognition system 60 with radar system 10. Recognitionsystem 60 includes an interrogating transmitter, a receiver for replysignals from equipment responding to the interrogator, a separatereceiver and responding transmitter for replying to other interrogators,and a lobe switching antenna system 61 for the interrogator and itsreceiver. Square wave 47 is applied to terminal 62 to blank the receiverfor the responding transmitter so that it will not be triggered by itsown interrogator. Square wave 47 is also supplied to multivibrator 68whose output square wave 69 is applied to displace horizontallyalternate sweep traces of the recognition display on A-scope 11.Positive trigger 51 is applied to terminal 63 to trigger theinterrogating transmitter. Square wave 53 is applied to terminal 64 tounblank the receiver for reply signals from equipment responding to theinterrogator. The dotted line between antenna 61 and 60 cycle A. C.source 29 indicates that source 29 controls the 6G cycle lobe switchingof the antenna beam.

Returning to multivibrator 28, it is triggered by the positive triggersof wave 26 and supplies a negative gate 70 to the control grid of thepentode of selector 71 whose constitution is similar to that of selector48. Positive triggers 18 are supplied to the screen grid of the pentodeof selector 71, whose output wave 72 triggers unit 75, comprisingmultivibrator and cathode follower stages, supplying square wave 76 toterminal 77 of radar system to blank the radar system 011 whenrecognition system 60 is operating. On the face of A-scope 11 as shownin Fig. 1, 78 is the radar trace and 79 is the recognition trace.Positive pip 80 is the echo of a target responding to interrogation. Thenegative pips 81 and 82 are the amplitude matched pips of therecognition signals in each lobe of the recognition antenna system 61,with the first pip 81 coming directly under the target 80 which itidentifies.

Selector 25 comprises pentode tube 90, a source of plate potentialconnected at terminal 91, screen resistor 92 connected at one end toground, cathode resistor 93 similarly connected to ground, and a sourceof positive cathode bias connected at terminal 94 and coupled throughresistor 95 to the cathode. Terminal 27 ties to the control grid of tube90. The 120 cycle wave 32 is coupled to the screen grid of tube 90through capacitor 33. The output from selector 25 is taken from thecathode of tube 90 to trigger multivibrator 38. Selector 48 comprisespentode tube 100, plate resistor 101 coupling the plate to a source ofplate potential connected at terminal 102, screen resistor 103 couplingthe screen to the ground, capacitor 104 coupling wave 18 to the screengrid, capacitor 105 coupling the output of multivibrator 46 4 leakresistor 106 connected beground. The cathode of tube 49 is taken fromits to control grid, and grid tween control grid and 100 is grounded andoutput wave plate.

In Fig. 2 are shown the wave forms at various points of the circuit ofFig. 1 in their proper time relationships. By reference to these waveforms and the circuit of Fig. 1, the operation of the system forcoordinating the radar and recognition systems will be readilyunderstood.

The modulator of radar system 10 supplies a negative trigger wave 16with a repetition frequency of 800 per second. This trigger 16 issynchronous with the pulsing of the radar transmitter and the start ofeach horizontal sweep of A-scope 11. From trigger 16 is to be derived,by synchronizer 19, the trigger 51 for pulsing the interrogatingtransmitter of recognition system 60 at a repetition frequency of 120per second. The individual triggers of the wave 16 are numbered from 1to 14 for fixing time relationships of the chain of wave forms in thecircuit of Fig. 1. Unit 17 takes each negative trigger 16 from themodulator and inverts it to supply positive trigger 18 to multivibrator20. Each trailing edge of square wave 21 is coincident with an oddnumbered trigger of wave 18, starting with trigger 1. The constants ofmultivibrator 20 are such that the leading edges of square wave 21 eachprecede the even numbered triggers of wave 18. Square wave 21 isdifferentiated by capacitor 22 and resistor 23 to produce trigger wave26, having negative triggers coincident with the odd triggers of wave 18and positive triggers preceding the even triggers of wave 18.Multivibrator 28 responds only to the positive triggers of 26 andprovides a negative gate 70 which is then centered about the eventriggers of wave 18. Selector 71 is a pentode biased to zero gridvoltage and has negative gate 70 applied to its control grid and wave 18applied to its screen grid. All even numbered triggers of wave 18 arerejected because the control grid is negative when they appear on thescreen grid and hence only odd numbered triggers appear in output wave72. Block is triggered by each pulse of wave 72, generating square wave76 whose positive gate unblanks the receiver of radar system 10. Thus,the radar display appears on A-scope 11 following odd numbered triggersof wave 18 and at a repetition rate of 400 cycles.

The even numbered triggers of wave 18 are reserved for triggeringrecognition system 60 according to the control frequency of 60 cycle A.C. source 29. Rectified 6O cycle wave 32 has its D. C. component removedby capacitor 33 as shown by wave 34, where the dashed line is the D. C.level. Wave 34 is applied to the screen grid of pentode of selector 25,whose control grid receives wave 26. Pentode 90 is biased to cut-oil andconducts only when the control and screen grids are driven positivesimultaneously. Output wave 37 of selector 25 corresponds to all evennumbered pulses of wave 18, since the positive pulses of wave 26 are alleven numbered. It will be noted that each trigger of wave 37 precedesthe corresponding trigger of wave 18 by the amount established bymultivibrator 20 in generating square wave 21. Also, for each half cycleof the 60 cycle supply, or each cycle of wave 34, there are either oneor two triggers in wave 37. Unit 38 is a multivibrator which istriggered by the first trigger of wave 37 that appears at its input toinitiate a pulse of a recurrent-pulse signal, square wave 39. Thepositive gate or width of the resulting square wave 39 is adjusted toextend beyond the next trigger of 37 if there should be a second one inany cycle of wave 34, as shown. Thus multivibrator 38 is renderedunresponsive to all but the selected first appearing trigger of wave 37.Square wave 39 after differentiation by capacitor 40 and resistor 41becomes trigger wave 42. only to the positive pulses of wave 42 and itsoutput square wave 47 has a positive gate which is centeredMultivibrator 46 responds about one even numbered trigger of wave 18 foreach cycle of 120 cycle Wave 34.

Selector 48 containsanother selector pentode 100 which is biased tocut-off. Square wave 47 is fed to its control grid and triggers 18 toits screen grid. Only a trigger of wave 18 which occurs during thepositive gate of square wave 47 will result in an output from pentode100, as shown in wave 49, and this output will correspond in time toone'evennumbered trigger of wave 18 during each cycle of 120 cyclecontrol wave 34. Thus a trigger 51 is provided for the interrogatingtransmitter of recognition system 60 by inverting trigger 4? in unit 59.

The derivation of trigger 51 from trigger 18 clemonstrates how thisinvention provides for the derivation of an electric pulse of a lowrepetition rate from a pulse of a high repetition rate. It will be notedalso that although triggers 51 and 18 are of nonintegral repetitionfrequencies, each trigger of 51 coincides with a trigger of the higherrepetition rate trigger 18 and, in this sense, synchronism is achieved.

Simultaneously with the triggering of the interrogator of recognitionsystem 60, trigger 51 triggers multivibrator 52 to generate square wave53 whichis applied to terminal 64 of recognition system 60 to provide anunblanking gate for its interrogator receiver. To provide the lobeswitching displacement of the horizontal recognition trace on the'Aescope 11, square wave 47 is supplied to multivibrator 63 whichgenerates a gate 69 having half the repetition frequency of wave 47 andoccurring at every other pulse of interrogator trigger 51. By the termgate as used in this specification is meant a voltage pulse used forgating or otherwise controlling the operation of a succeeding circuit.By applying this gate 69 to the cathode of the tube supplying the sweepof A-scope 11, alternate sweeps forthe recognition trace are displacedhorizontally, which is the desired presentation for lobe matching.

The resultant presentation on the face ofA-scope 11 was described inconnection with Fig. 1.

It will be noted that in addition to its primary function in thisinvention as a deriver of a pulse of lowrepetition frequency from apulse of higher repetition frequency, synchronizer l9 providesgates andtriggers for other functions in coordinating the operation of radarsystem to and recognition system 61%., For example, multivibrator 20 isemployed as. a two-to-one' divider to provide, among other things, forradar and recognition system sharing of A-scope 11 presentation onalternate triggers of wave 18., However, it is readily apparent thatmultivibrator 2E9, capacitor 22, and-resistor 23are not essential tothis invention since triggers 18 could be applied directly to selector,25. Furthermore, the repetition rates of square wave 39, square waved?and trigger 51 are the same so that square wave 39 could be directlyutilized as the derived-low frequency signal according to thisinvention, the synchronizer then being further simplified by theelimination of capacitor it), resister 41, multivibrator 46,and selector4%. 7

From the foregoing description, it will be readily seen that thisinvention provides'azcircuit for deriving an electric pulse signal ofnonintegral and relatively low repetition rate from a pulse signal of ahigher repetition rate. Although there is shown and described only acertain specific embodiment of this invention in a coordination system,the many modifications possible thereof will be apparent to thoseskilled in the art. Therefore, this invention is not to be limitedexcept in so far as is necessitated by the prior art and the spirit ofthe appended claims.

What is claimed is:

l. A coordination system for preventing interference between a radiopulse echo detection system and a co operating lobe-switched antennadirectional recognition system having at least one transmitter and onereceiver using a common cathode ray indicator comprising, a source ofvoltage pulses having a known constant repetition rate, a frequencydivider responsive to pulses from said source to produce two series ofpulses, the pulses of the first of said series occurring in timecoincidence with alternate pulses from said source, the pulses of thesecond of said series being spaced from pulses of said first series ofpulses by a predetermined time interval, means to control the operationof said radio pulse echo detection system in response to pulses of thefirst of said series, a power source for switching said antenna lobes,means responsive to voltage from said power source and said secondseries of pulses to select one of said second series of pulses for eachswitching cycle, means to control the operation of said recognitionsystem in response to each selected pulse from said second series, meansresponsive to pulses from said second series to render the receiver ofsaid recognition system operative immediately following the timeinterval of operation of its transmitter, and means responsive toalternate selected pulses from said second series to displacehorizontally the indication of said cathode ray indicator duringalternate switching cycles of said lobe-switched antenna.

2. In a combined microwave radar search system and cooperating directiveradio recognition system employing a common indicator, a circuit forcoordinating and synchronizing the operation of the components of thecombined system comprising an alternating current power source forswitching the directivity of said recognition system, a source ofvoltage trigger pulses having a known constant repetition rate, meansresponsive to trigger pulses from said source to produce two series ofpulses, pulses of the first of said seriesoccurring in time coincidencewith odd numbered trigger pulses from said source, pulses of the secondof said series occurring a predetermined time interval before evennumbered trigger pulses from said source, means to control the operationof said radar system from the first of said series of pulses, means forderiving a unidirectional cyclic control voltage from said alternatingcurrent power source, means responsive tothe second of said series ofpulses and to said cyclic control voltage to select a single pulse ofsaid second series for each cycle of said control voltage, and means forcontrolling the operation of said recognition system from the selectedpulse of said last-named selecting means.

3. In a combined microwave radar search system and cooperating directiveradio recognition system employing a common indicator, a circuit forcoordinating and synchronizing the operation of the components of thecombined system comprising, an alternating current power source, meanscontrolling the directivity of said recognition system from said powersource, a source of voltage trigger pulses having a known constantrepetition rate, means responsive to trigger pulses from said source toproduce two series of pulses, pulses of .the first of said seriesoccurring in time coincidence with odd numbered trigger pulses from saidsource, pulses of the second of said series occurring a predeterminedtime interval after odd numbered trigger pulses from said source, meansto control the operation of said microwave radar search system from thefirst of said series of pulses, means for deriving a unidirectionalcyclic control voltage from said alternating current power source, meansresponsive to the .second of said series of pulses and to said cycliccontrol voltage to select a single pulse of said second series duringeach cycle corresponding to a period of directivity of said antenna,meansto control the operation of said recognition system from saidselected pulse, and means for controlling the position of the display ofsignals from said recognition system on said indicator to distinguishthe signals from each directional position of said antenna.

4. A circuit for coordinating and synchronizing the operation of acombined microwave radar search system and a directional radiorecognitionsystem comprising a source of timing pulses having a knownrepetition rate, an alternating current power source for switching. thedirectiyity or said'recognition system;,means responsive to pulses fromsaid source oftirning pulsesfor controlling the operation of, saidsearch system on alternate timingpulses,

means responsive to voltage from, said alternating current power sourceto derive acyclic control' voltage syn chronous with said switching,means responsive to said control voltage and the remaining-timingpulsesfromsaid source toselect a singleitiming pulse during each'switchedposition of directivity, and means whereby each of said selected pulsescontrols the operation of'said recognition system.

5. A circuit for-coordinatingand synehronizingtheop; eration of acombined microwave radar search system and a directional radiorecognition system comprising a source of timing pulses having aknownrepetition rate, an alternating current power source for switchingthedirectivity of said recognition system, means responsive to pulses fromsaid source of timing pulses for controlling the operation of saidsearch system on alternate timing pulses, means responsive to voltagefrom said-"alternating current power source to derive acyclic control'voltagesyn chronous with said sw1tching, means responsive to saidcontrol voltage and the remaining timingpulses from said: source to.select a single timing pulseduri ngeach switched position. ofdirectivity, means] whereby each'of said selected pulses controls. the.operation of said recognition system, and means for rendering thereceivers of each 1 system operative only during the time intervalbetween timing pulses following the pulsedoperation of'their re-,spective. transmitters.

6. A circuit for coordinating and synchronizing the operation of acombined: microwave radar search system and, a directional radiorecognition system comprising a source of timing pulses having a knownrepetition rate, an alternating. current power source for switching. thedirectivity of said recognition system, means responsive to pulses fromsaidsource of timing. pulses for controlling the operation of said,search, system on alternate timing pulses, means responsive to voltagefrom said'alternating current power source to derive a cyclic controlvolt'agesynchronous with said switching means respon: sive to saidcontrol voltage andfthe remaining timing pulses of said source to selecta single timing pulse during each switched position of, directivity,means whereby each of said selected pulses controls. theoperation ofsaid recognition system, means for renderingf'the receivers of eachsystem operative'only during the time interval between timing pulsesfollowing the pulsed operation of their respective transmitters, acathode ray indicator common toboth systems, and means for displacingtheposition of said ray to distinguish the signals from each directivity ofsaid recognition system.

7. In a combined microwave radar search system and cooperatingdirectional lobe-switched antenna radio recog: nition system using acommon cathode ray indicator, a circuit for coordinating andsynchronizing the operationof the components of the combined systemcomprising, a source ofrepetitive trigger voltage pulses, a frequencydivider responsive to pulses from said source for producing an outputsquare wave havingpositive'portions of longer time duration thanthe/negative portions, a derivative circuit responsive to the output ofsaid frequency divider for producing negative pulses in'time coincidencewith odd pulses from said source and positive pulses preceding in timeby a predetermined time interval the even pulses from said source, afirst multivibrator responsive to positive pulses from said derivativecircuit to'produce a square output'wave having-a negative portionofdouble said predetermined time interval centered about said even pulsesfrom said source, a first selector circuit responsive to pulses fromsaid source and the output wave of said'first'multivibrator to rejecteven pulses from said'source and to produce an. output pulse in timecoincidence with every oddpulse from said source, means responsive tothe output pulse of said first selector circuit to produce an outputsquare wave having a positive portion of time duration for the controlof the operation of said microwave radar search system within the periodof said pulse source, a source of alternating current power energizingthe lobe switching mechanism of the directional antenna. ofsaidrecognition system, means responsive to voltage from said alternatingpower source to produce a control voltagerwave having a cycle for eachantenna switching position, means responsive to time coincidence ofpositive pulses. from said derivative circuit and to said control signalvoltage. wave to produce output pulses preceding by saidpredeterminedtime interval an even pulse from said source of trigger voltage pulsesand coincident with a cycle of said control voltage, a second.multivibrator responsive to the first coincident pulse from saidlast-named means to generate an output square wave having a timeduration. including subsequent pulses from said last-named meanscoincident with a single cycle of said control voltage, a secondderivative circuit responsive to the output of said second multivibratorto produce single positive pulses in time coincidence with each cycle ofsaid control voltage and preceding by said predetermined time intervalan even pulse from said source of trigger voltage pulses, a thirdmultivibrator responsive to positive pulses from said second derivativecircuit to produce a square wave having a positive portion of doublesaid predetermined time interval and centered on an even pulse. fromsaid source of trigger pulses for each cycle of'said control voltage, asecond selector circuit responsive to. the output of said thirdmultivibrator and pulses from said source of trigger voltage pulses toreject odd. pulses from said source and to produce one output pulse intime coincidence with an even pulse from said source during each cycleof said control voltage, means applying the output'pulses from saidsecond selector circuit to energize said recognition'system transmitter,a fourth multivibrator responsive to the output pulses of said secondselector circuit to generate an output square wave having a positiveportion time duration less than the period of said trigger pulses, meansapplying the output square wave of said fourth multivibrator to controlthe operation of the receiver of said recognition system, a fifthmultivibratoroperating as a scale of two frequency divider responsive tooutput pulses from said third multivibrator to generate a squarewavehaving a positive portion in time coincidence with alternate outputpulses of said fourth multivibrator, and means applying the output ofsaid fifth multivibrator for the horizontal displacement of alternatesignals from said recognition system for ease of matching signalsfrom'each lobe of said recognition system antenna.

References Cited in the file of this patent UNITED STATES PATENTS2,515,178 Barchok July 18, 1950' 2,540,087 Barchok et al Feb. 6, 19512,586,888 Varela Feb. 26, 1952

